I happen to have a copy of that one...
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How flat is flat?
- Thread starter daftcombo
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OP
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Could you correct to stay in a 1dB window?
How did you measure that? Can you post that measurement here?
Sure, I can fix a mic at my LP, do a single sweep, invert the response to create a filter and when measuring again I will have response within 1.5dB window - but it will sound awfull. Once you do a proper linearisation of the in-room response based on spatially averaged measurements it will sound good, but it won't be within 1.5dB window when you measure it again.
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I could but I don't like to go crazy with EQ above the transition frequency, the LS50's mostly just need the region from 2-5k brought down a bit and a slight cut around 750, slight boost around 1500.
Right, it wouldn't work using the room curve, I only EQ above the transition frequency using anechoic measurements if possible. I brought in the listening window from Soundstage's measurement and corrected the response, the Klippel measurement would be fine too but the 5k peak isn't evident in any of my in-room measurements so I trust Soundstage more in this case.
Even if we ignore room effects there is a difference between samples - your speaeker will not have identical response as the speaker tested by Soundstage.
I've had 3 pair of LS50 now and all 6 speakers were pretty close to each other so I'm not sure that's actually a real problem or maybe LS50s have better quality control than cheaper speakers. Either way you're right that no method is perfect but it's the we've got so it's what I go with.
Sure, one would expect inter sample variations are small with quality speakers like LS50.
NoAudiophile
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Every speaker designer I've ever talked to has assured me that their speakers measure flat. Flat can be defined in a multitude of ways, unless you are dealing with perfect constant directivity, a +-0db on-axis speaker will not be 'flat'. Currently regardless of who you purchase a pair of speakers from, or how much you paid, you can always do better correcting them yourself - if you know what you are doing.
Here are my 10 steps to achieve a "flat" speaker and room combo for one listening position:
1. All measurements for corrections are done windowed outside for treble on the tweeter axis
2. All bass measurements for corrections are done using 2 meter ground plane method outside - do not window this measurement down.
3. Splice the two measurements together and correct flat +-0.5dB to at least 50Hz
4. Remeasure off axis(0,5,10,15,30,45,60 degrees horizontal and 0,5,10,15,30 vertical) treble response outside with correction applied.
5. Average the results of the second round of measurements, any irregular dips or peaks that do not follow the slope in average treble should be adjusted minimally to within +-1.0dB of the natural directivity slope of the speaker, compromising the on-axis response for a smooth weighted power response.
-- You can stop at this point if you want a pure "flat speaker" and let the room do what it wants, otherwise continue --
6. Place corrected speaker in final position for best imaging, measure speaker with the mic pointed in listening position at ear level pointing at the speaker - do not window this measurement down.
7. Take 1:1 smoothing response and keep as baseline tone.
8. Adjust only below 500Hz or Schroeder frequency(where you think the room becomes modal) removing only peaks in the response with whatever Q filters you need to do the job - do not remove floor bounce.
9. Remeasure the speaker from the listening position with correction applied.
10. Use 1:1 smoothing response of measurement and raise it with broad filters to match the previous baseline 1:1 measurement.
Notes:
All of these steps should be performed for each speaker independently. The last step is probably the most overlooked and important.
A minidsp will probably run out of filters halfway through this method, so as you go there will need to be a refactoring of filters to reduce their number which attempting to maintain the effect.
Here are my 10 steps to achieve a "flat" speaker and room combo for one listening position:
1. All measurements for corrections are done windowed outside for treble on the tweeter axis
2. All bass measurements for corrections are done using 2 meter ground plane method outside - do not window this measurement down.
3. Splice the two measurements together and correct flat +-0.5dB to at least 50Hz
4. Remeasure off axis(0,5,10,15,30,45,60 degrees horizontal and 0,5,10,15,30 vertical) treble response outside with correction applied.
5. Average the results of the second round of measurements, any irregular dips or peaks that do not follow the slope in average treble should be adjusted minimally to within +-1.0dB of the natural directivity slope of the speaker, compromising the on-axis response for a smooth weighted power response.
-- You can stop at this point if you want a pure "flat speaker" and let the room do what it wants, otherwise continue --
6. Place corrected speaker in final position for best imaging, measure speaker with the mic pointed in listening position at ear level pointing at the speaker - do not window this measurement down.
7. Take 1:1 smoothing response and keep as baseline tone.
8. Adjust only below 500Hz or Schroeder frequency(where you think the room becomes modal) removing only peaks in the response with whatever Q filters you need to do the job - do not remove floor bounce.
9. Remeasure the speaker from the listening position with correction applied.
10. Use 1:1 smoothing response of measurement and raise it with broad filters to match the previous baseline 1:1 measurement.
Notes:
All of these steps should be performed for each speaker independently. The last step is probably the most overlooked and important.
A minidsp will probably run out of filters halfway through this method, so as you go there will need to be a refactoring of filters to reduce their number which attempting to maintain the effect.
She may be flat, but man what a set of stems!
Some miniDSP will accept FIR filters, which don't seem to have a limit on the wiggles that can be produced, but aren't appropriate for low frequencies (use the PEQ or biquads) due to the limited number of taps.
Example FIR generated by AcourateDRC for the miniDSP OpenDRC-DI:
AcourateDRC then creates biquads for PEQ filters for the low frequencies and for broad strokes.
Combine those responses for the final filter.
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I do not know of many speakers that are able to achieve +/-1.5dB. Probably only Genelecs... any other ones?
renaudrenaud
Major Contributor
D&D 8c, Kii Three, JBL M2, Revel Performa M20, Adam S2V come to my mind at this moment.
I seriously doubt you heard a 0.1dB difference, even if its broadband. That is an EXTREMELY minimal change.
I did not say I heard a 0.1dB difference... Read the post. I said a couple of people noticed it. I was the joker who changed the HF level in the studio by 0.1dB while they were out... Also read the literature, there are numerous papers and examples of people noticing a 0.1dB difference - Bob Katz said he could not believe his new DAC (a Prism or Craneson I think) sounded SO much better than his old one, more detail etc etc, until he checked levels properly, and found it 0.1dB hotter than his old DAC (probably an Avid). When he had the levels exactly the same he said he could not hear any difference between the DACs. No one hears a 0.1dB change as a level change, we notice it in other ways, "detail", "presence", "clarity" etc etc.
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solderdude
Grand Contributor
Anecdotal:
I have never been able to do that (-0.1dB at 20kHz) but successfully blind tested a -0.5dB drop-off at 20kHz in my younger years.
It was not perceived as rolled-off or less bright but when the roll-off was present the sound appeared 'fuller' somehow.
This was in the days of the Johan Ketelaar CD filter. He claimed his filter (12dB/octave) was better than the steep filters used in CDP's.
The intention was you remove the analog post filter (or tap off before the filter) and use the transistor based simple filter.
Most CDP's in those days were 4x or 8x oversampling so most of the reconstruction filtering was done digital anyway so gentler slope post filters could be used (a great advantage of oversampling)
All kinds of audiophile claims were made in magazines in that time. Fortunately the schematics were printed somewhere so I built me one.
Of course in that day I still did most comparisons sighted. I could also switch between outputs (original and JK filter) making comparisons easy.
I could hear differences between the 2 filters. Also when tested blind (someone else flipping the switch) but was harder.
I became intrigued by this and measured the response (which was the same as the published one) and connected the filter behind the normal post filter. The difference was still there. Obviously the gentle roll-off (-0.5dB at 20kHz) started slowly at 10kHz. That roll-off and possibly (not measured) phase response ? seemed responsible for the effect.
My ears are too old now so the effect is gone for me now.
Still think my hearing hasn't gotten worse while objectively it is a lot worse.
So whenever I see a gentle roll-off in the audible band showing -0.5 to -1 dB drop-off at 20kHz I know some (younger) folks can hear this but won't hear it as roll-off but as fuller sounding.
I have never been able to do that (-0.1dB at 20kHz) but successfully blind tested a -0.5dB drop-off at 20kHz in my younger years.
It was not perceived as rolled-off or less bright but when the roll-off was present the sound appeared 'fuller' somehow.
This was in the days of the Johan Ketelaar CD filter. He claimed his filter (12dB/octave) was better than the steep filters used in CDP's.
The intention was you remove the analog post filter (or tap off before the filter) and use the transistor based simple filter.
Most CDP's in those days were 4x or 8x oversampling so most of the reconstruction filtering was done digital anyway so gentler slope post filters could be used (a great advantage of oversampling)
All kinds of audiophile claims were made in magazines in that time. Fortunately the schematics were printed somewhere so I built me one.
Of course in that day I still did most comparisons sighted. I could also switch between outputs (original and JK filter) making comparisons easy.
I could hear differences between the 2 filters. Also when tested blind (someone else flipping the switch) but was harder.
I became intrigued by this and measured the response (which was the same as the published one) and connected the filter behind the normal post filter. The difference was still there. Obviously the gentle roll-off (-0.5dB at 20kHz) started slowly at 10kHz. That roll-off and possibly (not measured) phase response ? seemed responsible for the effect.
My ears are too old now so the effect is gone for me now.
Still think my hearing hasn't gotten worse while objectively it is a lot worse.
So whenever I see a gentle roll-off in the audible band showing -0.5 to -1 dB drop-off at 20kHz I know some (younger) folks can hear this but won't hear it as roll-off but as fuller sounding.
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OP
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Sounds a like a good method, especially step 10. which prevents the bass from being to shy. But it seems to me like not a lot of bookshelf speakers (maybe none, actually) can be corrected to flat down to 50 Hz without bottoming out or struggling like crazy even at moderate volume, especially if you also give a boost thanks to that step 10.
NoAudiophile
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DSP active speakers of even the smallest variety hit 50Hz flat. iLoudMM being the smallest, but there is also Vanatoo Transparent Zero as well as larger options like the JBL LSR305. The port tuning on a speaker may need to be adjusted in some cases, but if you put a sharp cut (48db/octave or more) after 50Hz you can get just about any speaker to play flat to 50Hz with a good amount of headroom left.
If a speaker can't do the job of playing to 50Hz flat at the volume that I need, then it's not really a complete speaker IMO.
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